International trade is complicated.

Say we have 3 countries;

Country A

• has companies that produce steel
• has a manufacturing base that consumes steel
• has trade agreements with country B, and country C on steel trade providing lower than normal tarrifs

Country B

• has companies that consume steel

Country C

• has companies that produce steel

It's possible that country A's steel producers can make easier, or even higher profits selling steel in bulk to country B than if they were to service their manufacturing base.

At the same time, their manufacturing base could get cheaper steel from country C if, for example, it costs them less to make it.

Companies in country B, can't trade with companies in country C at the same cheaper rate, because the countries don't have a trade agreement setting lower costs on the steel trade for whatever reason.